The present invention relates to devices for monitoring the condition of tires. More particularly, it relates to systems for feeding energy to the different stages of those of the devices which have an electrical energy supply on the wheel.
The behavior of a tire is complicated; the monitoring cannot be reduced to the mere detection of one or more threshold values. It is therefore important to be able to transmit the measurement of one or more variables observed on the wheel, which is movable in rotation, to the chassis of the vehicle, and this preferably for any angular position of the wheel. When active components are used on the wheel in order to effect the necessary measurements, it is indispensable to provide an energy feed on the wheel. The energy required can be supplied either by a battery or a condenser of sufficient capacitance, charged by any suitable means. An example of the use of a battery is found in the tire-monitoring device proposed in French Patent Application No. 2,529,513. An example of condenser charging is found in European Patent No. 45,401, in which the electrical energy is transmitted from the chassis towards the wheel by inductive coupling between two coils one of which is fastened to the chassis and the other to the wheel.
In a tire-monitoring device of the type having active components, there may be on the wheel an energy storage stage (battery or condenser with its charging means), a converter stage for transforming the value of the variables measured into an electrical signal, and a stage for the transmitting of the signal. This transmission stage is a power stage as compared with the converter stage, that is to say a stage which utilizes a sufficiently large amount of electrical energy to assure the transmission of the signal from the wheel to the chassis, in general by inductive coupling.
Whatever the system employed for the storage of the energy, it is important to minimize the consumption of electrical energy on the wheel as much as possible. This is important if battery feed has been provided in order to avoid having to replace the battery prematurely, and it becomes entirely crucial if the device obtains its energy from a condenser. The conventional precautions used up to the present time are limited in most cases to using components of low energy consumption, for instance, those utilizing CMOS technology.